Two dimensional (2-D) real- time phased array ultrasound has become a dominant medical imaging modality due to low costs, high efficacy and the absence of ionizing radiation. Real- time phase array volumetric scanning systems (often called "4D Ultrasound Systems) promise an array of enhanced diagnostic capabilities, and will therefore replace 2-D phased array ultrasound as the dominant ultrasound modality, especially in cardiology applications. The applicant organization owns the patent for the only known effective mechanism for implementing 3-D real-time ultrasound images. The applicants proposed to develop a commercial fully featured scalable real time phased array volumetric scanner. The basis for this machine will be the real time phased array volumetric scanner at Duke University. Mixed analog/digital signal processing will be used to reduce the power consumption of the Duke system by a factor of ten, the physical size by a factor of four and the cost basis by a factor two. The resultant system will be portable, will plug a single 120v 20amp wall socket, and will have a cost competitive with that of existing commercial 2-D phased array ultrasound machines. Within these physical constraints the number of transmitters will be increased by a factor of two and the number of receive processors by a factor of eight over the current system. Phase I of this research was directed toward the design, construction, and testing of a unique phased array receiver system based upon a custom VLSI mixed signal delay line chip. The verification of adequate performance of this system in terms of signal to noise, dynamic range, linearity, signal delay, power consumption, size and cost was essential prior to the design and construction of the complete real time volumetric imaging system in Phase II.